The pyrethroids include naturally occurring and synthetic esters of chrysanthemummonocarboxylic acid (i.e. 2,2-dimethyl-3-(2'-methylpropenyl)-cyclopro- pane-carboxylic acid) or chrysanthemumdicarboxylic acid (i.e. 2,2 -dimethyl-3-(2'-carboxypropenyl)- cyclopropane-carboxylic acid) and are widely used as insecticides. The most important naturally occurring pyrethroids are Pyrethrin I and II which are the major active insecticidal principles of pyrethrum. Pyrethrin I is the pyrethrolone (i.e. 4-hydroxy-3-methyl-2-(2',4'-pentadienyl)-2-cyclopenten-1-one) ester of chrysanthemummonocarboxylic acid and Pyrethrin II is the pyrethrolone 3-ester of chrysanthemumdicarboxylic acid-1-methyl ester. Pyrethrum also contains as minor active insecticidal principles Cinerin I and Cinerin II, which are the 4-hydroxy-3-methyl-2-(2'-butenyl)-2-cyclopenten-1-one esters of chrysanthemummonocarboxylic acid and chrysanthemumdicarboxylic acid-1-methyl ester respectively. Pyrethroids have low mammalian toxicity because they are relatively easily metabolized by warm-blooded animals and hence have found widespread acceptance as insecticides.
Some medical uses have been proposed for certain pyrethroids but, to the best of our knowledge, the majority of such uses have been directly related to their known insecticidal properties. The medical uses presently known to us are briefly acknowledged below.
Pyrethrum has been used as an active ingredient in an ointment for the treatment of scabies, which is a contagious skin infection caused by the mite Sarcoptes scaboi (see The Merck Index, Eighth Edition, 1968). Further, pyrethrum has been used in insect repellent creams (see the Extra Pharmacopoeia, Martindale, Twenty- fourth Edition, 1958) and in external preparations for the treatment of body lice, especially head lice (see "A 200 Pyrinate" and "Rid", The Physicians Desk Reference 1982). In this connection, UK Patent Specification No. 2072013 (published 1981) describes improving the activity of pyrethroids in the treatment of body lice by using them in conjunction with vegetable oils and/or detergents.
It has been proposed to use certain synthetic pyrethroids in the veterinary treatment of various forms of mange and ticks by oral, parenteral and topical routes (see US Pat. No. 4100297 issued 1978).
It was proposed in 1936 (see UK Patent Specification No. 447949) to use a pyrethrum containing composition in the treatment of gonorrhoea and dental suppurating diseases. The composition comprises a petroleum ether, or similar, extract of pyrethrum together with perilla aldehyde in an organic solvent. The perilla aldehyde was obtained from oil of perilla treated so as to eliminate limonene and pinene and other impurities. We understand that oil of perilla is obtained from a type of mint plant.
More recently (1959), it has been reported that pyrethrin extracts of Chrysanthemium cinerariaefolium have muscle relaxant properties as tested using guinea pig and rat ileum (see Chemical Abstracts, 53, 4570f).
Surprisingly, it has been found that pyrethroids are effective at low doses in the treatment of a wide range of parasitic and viral diseases in humans, including amoebiasis, genital herpes, hepatitis, influenza, malaria and parotitis (mumps).